Question: Which of the following numbers is a factor of 98? ${3,7,9,10,13}$
Solution: By definition, a factor of a number will divide evenly into that number. We can start by dividing $98$ by each of our answer choices. $98 \div 3 = 32\text{ R }2$ $98 \div 7 = 14$ $98 \div 9 = 10\text{ R }8$ $98 \div 10 = 9\text{ R }8$ $98 \div 13 = 7\text{ R }7$ The only answer choice that divides into $98$ with no remainder is $7$ $ 14$ $7$ $98$ We can check our answer by looking at the prime factorization of both numbers. Notice that the prime factors of $7$ are contained within the prime factors of $98$ $98 = 2\times7\times7 7 = 7$ Therefore the only factor of $98$ out of our choices is $7$. We can say that $98$ is divisible by $7$.